From the late Neoproterozoic to the Triassic, the major blocks on the Earth experienced two breakup-assembly cycles of supercontinents: the breakup of Rodinia and the assembly of Gondwana, followed by the breakup of Gondwana and the assembly of Pangea ^[12] (Fig. 2). The interactions between multiple spheres of the Earth jointly controlled the formation of marine ultra-deep petroleum systems in the Sichuan and Tarim basins by regulating changes in terrestrial and mantle inputs, biological radiation and extinctions, the surface temperature of the Earth, sea level rise and fall, precipitation at different latitudes, positions of the South China and Tarim blocks and regional geological events ^{[12⇓⇓⇓⇓⇓-18]} (Fig. 3). Large-scale orogenic events (e.g., Pan-African, Caledonian, Variscan and Indosinian orogenies) enhanced continental weathering and erosion, resulting in a high influx of terrigenous sediments into the oceans (Fig. 3a-3b), and fixing atmospheric carbon dioxide (CO₂) ^[19-20]. The rift basins formed during the breakup of supercontinents received nutrient inputs from weathering and thereby motivated prolific productivities in oceans and on lands, which further fixed atmospheric CO₂ during the deposition of organic-rich sediments ^[21-22]. From the Cambrian to the Permian, active material migration between land and oceans and burial of organic carbon led to a long-term cooling trend, which triggered the Hirnantian and Carboniferous-Permian glaciations, and synchronous and significant sea level decline (Fig. 3c) ^{[15,21 -22]}. During anorogenic periods, e.g., the Ordovician, Devonian, and late Permian to early Triassic, terrigenous inputs were mainly controlled by sea level fluctuations, exhibiting a reverse-phase relationship ^[23]. In other words, sea level rise made terrigenous influx reduce, while sea level fall increased terrigenous influx (Fig. 3b, 3c). Notably, glacial environments could change the relationship between terrigenous inputs and sea level, causing a unique in-phase variation (Fig. 3b, 3c). This might be the influences from the cooling climate and the ice sheets that declined the sea level and reduced continental weathering, erosion and terrigenous influx ^[23].

During two transition periods from breakup to assembly, the Tarim and South China blocks were located on the margins of supercontinents and incorporated into supercontinents fairly late. Both of them experienced the evolution of Proto-Tethys, Paleo-Tethys and Neo-Tethys oceanic domains (Figs. 2 and 3a) ^[12]. As a result, rift basins formed along the margins of these blocks by the breakup of supercontinents could receive sediments for a long term. Subsequently, during collisional orogenesis or continental convergence, the early sedimentary sequences were buried deeper and became the present ultra-deep strata ^[6]. From the Cambrian to the Triassic, the South China and Tarim blocks drifted at middle-low latitudes for a long time, where the paleoclimate was mainly influenced by the Hadley Cell (Fig. 3d). Consequently, the marine ultra-deep petroleum systems in the two blocks share three key features. (1) They were all formed in cratonic rift basins during the transition from the breakup to assembly of supercontinents, e.g., the Deyang-Anyue Rift and Kaijiang-Liangping Rift in South China, and the North Depression in Tarim Basin. (2) They were formed during the post-glacial periods following global glaciations, such as the Cambrian Terreneuvian and Series 2 after the Neoproterozoic "Snowball Earth" event, the Silurian Llandovery after the Hirnantian glacial maximum, and the Permian Guadalupian and Lopingian after the Carboniferous-Permian glaciation. (3) The stratigraphic positions and development of source rocks, reservoirs, and seals were influenced by the locations of the rift basins within the Hadley Cell (Fig. 3c, 3e, 3f).

As the Gondwana supercontinent converged in the southern hemisphere, both the South China and the Tarim blocks obviously drifted southward during the Ediacaran‒Cambrian Period. The South China Block drifted from northern low latitude to the equator, while the Tarim Block drifted from near the equator to southern low latitude ^[12] (Fig. 3d). The jointing force of ocean-land distribution and the orbital obliquity of the Earth caused the intertropical convergence zone (ITCZ) of the Hadley Cell to shift northward during the Cambrian Terreneuvian and Series 2 periods ^[24]. Consequently, as the South China and Tarim blocks drifted southward through the humid, transitional and arid belts, organic-rich shales (e.g., the Cambrian Qiongzhusi Formation in South China and the Cambrian Yuertusi Formation in the Tarim Basin), microbial carbonates (e.g., the Dengying and Qigebulake formations of the Upper Ediacaran, the Canglangpu, Longwangmiao, Xiaoerbulake and Wusonggeer formations of Series 2), and evaporites (e.g., the Longwangmiao, Gaotai and Awatage formations of Series 2) were deposited (Fig. 3d-3f). At that time, the South China Block was located further north than the Tarim Block, and entered the humid zone later, resulting in later development of source rocks in the South China Block. Therefore, the sedimentary successions were developed in the Tarim and South China blocks during the southward drifting period, forming petroleum systems with Cambrian Terreneuvian‒Series 2 black shales as source rocks, Upper Ediacaran and Cambrian Series 2 carbonates as reservoirs, and Series 2 evaporites and shales as seals (Fig. 3e and 3f) ^{[25⇓⇓-28]}.

The Ordovician true polar wander event caused the rapid northward drifting of the South China and Tarim blocks from around 30°S ^[29]. Smaller than the South China Block, the Tarim Block entered the ITCZ humid zone earlier (Fig. 3d), and developed Ordovician Heituao and Tumuxiuke-Lianglitage formations source rocks (Fig. 3f). The Ordovician was a period when the sea level was globally highest but orogenic and volcanic activities were weak, limiting the influx of terrigenous clastic sediments (Fig. 3a-3c) ^[30]. The Tarim Block was largely inundated during the Ordovician, forming an extensive carbonate sedimentary platform and depositing Penglaiba, Yingshan, and Yijianfang limestones (Fig. 3f). However, the Heituao source rock was restricted to the deep-water depression in the eastern part of the Tarim Block ^[31]. As the Tarim Block drifted northward to 20°N, it entered the subtropical high-pressure arid belt in the northern hemisphere, and accompanied by the compressional uplifting of the Altyn Orogeny and significant terrigenous clastic influx, resulting in the deposition of the Upper Ordovician Sangtamu shales and Silurian clastic rocks (Fig. 3f). The South China Block was dominated by carbonate deposits during the Ordovician and did not enter the humid zone of ITCZ until the end of the Ordovician ^[17] (Fig. 3d). Influenced by the collision between the South China and the North China blocks and the formation of the Shangdan Suture Zone (Fig. 3a), the northern and western parts of the Sichuan Basin were uplifted to form paleohigh, while the northeastern and southern parts were depressed to the Wanzhou-Yibin paleo-Depression where source rocks of the Ordovician Wufeng Formation and Silurian Longmaxi Formation deposited ^[32].

The development of the Terreneuvian-Series 2, Ordovician and Longmaxi Formation source rocks corresponded to the rapid increases in biodiversity, namely the Cambrian explosion, the great Ordovician Biodiversification Event, and the rapid recovery after the Ordovician-Silurian mass extinction, respectively ^[14] (Fig. 3b). Favorable environmental factors for large-scale proliferation and radiation of lives included greenhouse or post-glacial warming environment, gradually rising sea level creating extensive shallow-water and oxygenated shelf environments (Fig. 3c), and enhanced internal Earth activities (e.g. orogeny and volcanism) supplying abundant nutrient elements (e.g., phosphorus) to the oceans while creating nutrient-rich environments (Fig. 3a, 3b), which ultimately promoted the diversification of phytoplankton and a surge in primary productivity ^[14,33]. The distribution of the Terreneuvian-Series 2 source rocks also exhibited a typical "Asian phenomenon" possibly due to the gradual termination of the Ediacaran glaciation, which strengthened the ocean thermohaline circulation in the Paleo-Asian, Proto-Tethys and Ural oceans (Fig. 2a), and led to the oxidation of dissolved organic carbon reservoir formed during the glaciation, the upwelling of deep-sea nutrients, and the massive release of carbon dioxide ^[34]. This process not only buffered the consumption of atmospheric carbon dioxide by organic carbon burial and continental weathering, and maintained the greenhouse condition during the intense continental weathering and erosion and large-scale organic carbon burial during the Terreneuvian and Series 2 (Fig. 3c), but also promoted rapid oxidation and nutrient cycling within oceans, providing necessary conditions for the surge in primary productivity and rapid evolution of lives, and ultimately favoring the massive production and preservation of organic matter ^[34]. During the late Cambrian and Middle Ordovician periods, the Proto-Tethys Ocean developed into an open ocean connecting the north and south poles (Fig. 2b) ^[12]. The continuously rising sea level and inundated platforms became more conducive to the development of carbonate rocks and biological radiation (Fig. 3b). The emergence and expansion of terrestrial vascular plants enhanced continental weathering, and maintained a high influx of terrigenous sediments and atmospheric CO₂ fixation when orogenic activities became weak. On the other hand, the expansion of eukaryotic algae in the oceans also increased the storage of organic carbon, further reducing the atmospheric CO₂ concentration, and ultimately leading to sustainable global cooling and triggering the Hirnantian glacial maximum ^[22] (Fig. 3a-3c).

The Ordovician true polar wander event initiated the overall northward drift of the Gondwana supercontinent and the marginal blocks, leading to the gradual closure of the Proto-Tethys Ocean and the expansion of the Paleo-Tethys Ocean (Fig. 3a). During the Permian to Triassic period, the converging Pangea supercontinent in the northern hemisphere and the Paleo-Tethys Ocean exhibited a south-north symmetrical distribution along the equator (Fig. 2c-2d) ^[35]. This tectonic configuration of land and sea induced symmetrical ocean currents within the Paleo-Tethys Ocean and a super-monsoonal pattern over the land, leading to alternating arid and humid climates at low latitudes with widespread evaporite and mudstone deposits (Fig. 3d), while mid-latitudes were semi-arid environment with abundant coal deposits ^[36-37]. The oxidation extents of the Permian atmosphere and ocean were significantly higher than those of the Ediacaran and Cambrian, even exceeding modern levels ^[38]. The dissolved organic carbon reservoir had already disappeared in the Permian deep sea ^[39]. The Permian marine and terrestrial biodiversity also reached the maximum level of the Paleozoic ^[14]. Without the balancing effect of the marine organic carbon reservoir, large-scale volcanic activities in the Permian, such as the successive Tarim large igneous province (TLIP), Emeishan large igneous province (ELIP), Siberian large igneous province (SLIP), and coeval terrestrial volcanism (Fig. 3a), had more significant impacts on global climate, carbon cycling, biological activities and source rock development ^[40].

The South China Block remained in the ITCZ during the Silurian−Permian periods and did not drift northward until the Triassic (Fig. 3d) when it collided with the North China Block, forming the Mianlüe Suture Zone (Fig. 3a) ^[4], and making the South China Block one of the blocks with the most abundant records of the Paleozoic life evolution ^[14]. However, during the Devonian-Carboniferous periods with sustainable global sea level declining (Fig. 3c), the Sichuan Basin underwent passive regression due to the lack of orogenic activities (Fig. 3a), leading to gradual expansion of land area and shrinkage of basin area ^[41-42]. In the late Permian, the South China Block drifted into the northern hemisphere, and the Emeishan mantle plume erupted along its southwestern margin (Fig. 2d). These have led to a tectonic pattern of "uplifts in the southwestern area, alternating uplifts and depressions in the central area, and rifts in the northeastern area" in the Sichuan Basin, and a progressive depositional pattern from terrestrial to transitional and then to marine from southwest to northeast, distinctly different from the depositional centers during the Terreneuvian-Series 2 and the Llandovery periods ^{[32,43 -44]} (Fig. 4). Simultaneously, the subduction of the Mianlüe Ocean induced regional extension and stretching, and created a series of northwest-southeast trending extensional faults which received widespread marine deposits in the Sichuan Basin during the late Permian and early Triassic period when the global sea level was declining (Fig. 3c). The newly opened Kaijiang-Liangping Rift became a deep-sea depositional area (Fig. 4) ^[43]. When the South China Block drifted northward across the ITCZ humid belt, source rocks of the first Member of the Maokou Formation (P₃m¹) and the Wujiaping−Changxing formations were developed, while in the transitional belt, carbonate rocks of the Qixia Formation, the second and third members of the Maokou Formation (P₃m²⁺³), and the Changxing- Feixianguan formations were deposited. After entering the arid belt in the early Triassic, gypsum salt rocks appeared in the Jialingjiang Formation. Ultimately, the "source-reservoir-seal" combination of the Permian-Triassic petroleum systems were formed (Fig. 3d-3e).

After reaching 30°N at the end of the Ordovician, the Tarim block remained in the arid belt for a long time until drifting northward again in the Permian, and colliding with the Junggar and Kazakhstan blocks to form the Tianshan Orogeny (Fig. 3a, 3d) ^[45]. Under intense compression, the North Depression of the Tarim block transitioned from a cratonic depression basin to a foreland basin and then to an intra-cratonic depression basin, gradually terminating marine deposition ^[31]. Consequently, the North Depression lacks marine source rocks from the Silurian to the Triassic (Fig. 3f), but has developed reservoirs and seals with high quality ^[9].

The Cambrian Terreneuvian-Series 2 source rocks that are widely distributed across the South China Block, but reach their maximum thickness within the Deyang- Anyue Rift play an important role in developing Anyue Gasfield and Taihe gas province. The formation of Deyang-Anyue Rift may be related to the regional Tongwan Movement in the late Ediacaran-early Cambrian periods, which led to freshwater leaching and dissolution modification of the Dengying Formation dolostones, effectively improving reservoir space, and created thick source rock in an anoxic condition within the rift during the subsequent marine transgression, establishing a good vertical and lateral contact with the dissolved Dengying dolostones ^[46]. As the rift was gradually filled, the distribution of platform marginal dolostone on grain-beaches and reef-shoals of the overlying Canglangpu and Longwangmiao formations increased significantly ^[6]. During the deposition of the Longwangmiao Formation, the Sichuan Basin was situated in an arid belt, and the top dolomites underwent karstification, improving reservoir quality and forming an overlying gypsum-salt seal ^[44]. Ultimately, a near-source source-reservoir-seal system with high quality formed around the Series 2 source rocks in the Deyang-Anyue Rift and the platform marginal belt. Since the formation of the Leshan-Longnüsi Paleo-uplift in central Sichuan due to late Silurian Kwangsian Movement, this region has remained in a relatively uplifted structural position, experiencing multiple burial and uplift events but still maintaining overall tectonic stability with significantly shallower burial depth than the northwest and east of the Sichuan Basin, exhibiting inherited uplift evolution ^[44] (Fig. 5a). Coupled with a lack of major fault disruptions, the source-reservoir-seal system in the central Sichuan has kept excellent sealing effects, facilitating the widespread distribution of Anyue Gasfield and Taihe gas province.

During the Terreneuvian, the Tarim Block experienced the Keping Movement, which was similar to the Tongwan Movement, leading to the formation of a "stacked" source-reservoir-seal system in the eastern depression, with the Terreneuvian source rocks overlying the Ediacaran dolostones and overlaid by the Series 2 dolostones and evaporites ^[6]. However, compared with the "enveloping-type" combination in the Sichuan Basin, the "stacked" source-reservoir-seal system had slightly poorer sealing integrity. It was prone to be disrupted by giant differential subsidence and major faults which were caused by the rapid compression during the Ordovician. And then, a series of steep and vertical fracture zones were formed in the brittle carbonate-dominated strata, causing the Cambrian and even Ordovician source rocks to rapidly enter the oil window in the North Depression (Fig. 5b). Generated hydrocarbons migrated upward along faults under buoyancy, and entered the Ordovician carbonate reservoirs ^[47]. In the Tarim Basin, the Ordovician is mainly composed of limestones that undergone certain degree of surficial karstification during deposition, and was further influenced by intense hydrothermal dolomitization during the deep burial stage ^[48]. Since dolostone has a stronger ability to preserve pores at deep burial than limestone, a high-quality far-source "channel-like" source-reservoir-seal system ultimately formed, with hydrocarbon provided by the Cambrian and Ordovician source rocks and sealed by the Upper Ordovician tight limestones and shales ^[6].

Since the Permian Guadalupian, continuous and intense LIPs has greatly influenced the global and regional tectonic environments and ecosystems ^[40], forming a microbe-metazoan transition (MMT). During that period, the microbial mediated carbonate depositional structures were almost a replication of the Cambrian MMT, indicating highly similar environmental and biological interaction between the two geological periods ^[49]. The combined effects of magmatic exhalation from the ELIP and extension due to the subduction of the Mianlüe Ocean resulted in the formation of the Kaijiang−Liangping Rift (Fig. 3a), which had a similar influence on the Permian- Triassic source-reservoir-seal system as the Deyang-Anyue Rift. Regional differential subsidence and sea-level fluctuations formed stacked rifts/sags and platform margins in the west and east of the Sichuan Basin, while progradational rifts/sags and platform margins were developed in the central Sichuan Basin ^[48]. Deep-water rifts, surficial karstification, and evaporite deposition enhanced the source rock quality, improved the carbonate reservoirs and optimized the seal integrity. In the west and east of the Sichuan Basin, such combination enabled the development of "enveloping-like" source-reservoir-seal system akin to the Dengying-Qiongzhusi-Longwangmiao formations e.g., the Qixia−P₃m¹−P₂m²⁺³, the Maokou-Wujaping + Changxing-Feixianguan + Jialingjiang formations, and received the upward migration of natural gas from the Qiongzhusi source rocks in the Deyang-Anyue paleo-Rift and the Wufeng-Longmaxi source rocks in the Wanzhou-Yibin paleo-Depression (Fig. 4) ^[51], forming far-source "channel-like" source-reservoir-seal system akin to the Tarim Basin.

The Cambrian was a pivotal period when the dominant life on the Earth transitioned from prokaryotic bacteria to metazoan ^[52]. Although eukaryotic algae had already appeared at least 1.7 billion years ago and had radiated in the Ediacaran ^[53], the distinctly negative organic carbon isotopic compositions (δ¹³C_org<‒30‰), abundant cyanobacterial fossils, and a suite of biomarker characteristics in the Cambrian Qiongzhusi source rocks indicate that prokaryotic bacteria (such as cyanobacteria) and eukaryotic algae were the most important sources of marine primary productivity ^[54-55]. Cyanobacteria sourced organic matter has been proven to be able to form oil-prone Type II₁ kerogen under anoxic and sulfidic conditions ^[56], consistent with the depositional environments and organic matter types of the Cambrian source rocks in the South China and Tarim blocks.

At the end of the Permian, the LIPs events led to catastrophic mass extinction for the already flourished eukaryotes, while the South China Block recorded a resurgence of cyanobacteria as the most important source of marine productivity after the eukaryotic extinction ^[57]. The volcanic-terrestrial-transitional-marine depositional pattern from southwest to northeast across the Sichuan Basin (Fig. 4), as well as the development of coal bed in transitional area ^[8], indicates that terrestrial plants had recovered after the ELIP event and provided terrestrial organic matter to the marine source rocks in the Kaijiang-Liangping Rift. Consequently, the Upper Permian source rocks contain mixed organic matter inputs including cyanobacteria, eukaryotic algae and terrestrial plants, consistent with their relatively heavy δ¹³C_org values (greater than −30‰), predominant Type II₂ kerogen, and a suite of biomarker characteristics ^[51].

The composition of organic matter and depositional environments determine that the marine ultra-deep source rocks in China are dominated by Type II kerogen with a high oil generation potential. They can generate a large volume of oil at the maturity (R_o) of 0.7%-1.3%, corresponding to approximately 90-150 °C of formation temperature. Higher temperature and maturity would cause further cracking of oil and kerogen to generate natural gas. However, higher pressure may suppress oil cracking to some extent, but favor oil preservation in ultra-deep formations ^[6]. Additionally, oil generation is the result of a kinetic mechanism of continuous chemical reactions that requires a certain geological period. Rapid oil generation at high temperature lasts 5-10 Ma, while slow generation at low temperatures may take 100 Ma or even longer. Therefore, the heat flow values and burial histories in the Sichuan and Tarim basins directly impact the hydrocarbon generation intensities and current petroleum compositions ^[50] (Fig. 5).

Prior to the eruption of the Emeishan mantle plume, the Sichuan Basin had been slowly subsiding at a low geothermal gradient for a long time ^[50], causing the Cambrian source rocks fail to effectively generate oil (Fig. 5a). The Emeishan mantle plume not only significantly elevated the heat flow values in the deep of the Sichuan Basin, but also led to the rapid burial of the Cambrian source rocks into the oil and gas windows ^[58], and reached ultra-deep realm after the Dongwu Movement (Fig. 5a). The Emeishan mantle plume also impacted the burial process and hydrocarbon generation of the Permian source rocks in the Sichuan Basin by modifying the thermal regime and deep structures. These modifications enabled the Permian source rocks in the northeast and northwest of the Sichuan Basin to rapidly entry into an ultra-deep environment and complete oil and gas generation ^[59] (Fig. 5a). The paleo-uplift region in the central Sichuan Basin entered the ultra-deep realm slightly later and had a smaller burial depth (Fig. 5a). However, due to its proximity to the Emeishan mantle plume, the deep geothermal gradient was higher than most other regions, which also led to extensive oil cracking into gas. Given the high atmospheric oxygen level and seawater sulfate content during the Permian, abundant sulfates adsorbed or co-precipitated in carbonates involve the thermochemical sulfate reduction (TSR) reaction under the ultra-deep and high temperature environment, further accelerating oil cracking into gas ^[60] (Fig. 5a). By the mid-Cretaceous, the Cambrian and Permian source rocks in the Sichuan Basin were generally buried at 6 000-10 000 m. The ultra-deep condition with high temperature for 100 Ma had led to complete cracking of oil into gas, even inducing the organic-inorganic hydrogenation process of over mature organic matter to generate gas ^[61] (Fig. 5a). The effect of the Himalayan Movement in the Sichuan Basin was mainly characterized by a lateral strike-slip in the orogenic belt and a thrust uplift in the western margin. On the other hand, it did not contribute to the generation of oil and gas, but impacted the preservation and accumulation of early gas ^[5].

In contrast, from the Cambrian to the Permian, the Tarim Block was influenced by the opening of the Paleo-Asian Ocean and crustal thinning at cratonic margins which resulted in higher heat flow values than those in the South China Block ^[59]. During the rapid burial in the Ordovician, some of the Cambrian source rocks (e.g., in the Manjiaer Sag) entered an oil window and even a gas window for a short time (Fig. 5b). From the Caledonian Movement to the Yanshan Movement, the Tarim Basin was compressed by the surrounding landmass, forming a tectonic sedimentary pattern with alternated uplifts and depressions (Fig. 6). The thermal evolution processes of the Cambrian source rocks were quite different among the North Tarim Uplift, the North Depression, and the Central Uplift ^[62]. In the Manjiaer Sag, the Cambrian-Ordovician sediments entered an ultra-deep realm with oil cracking into gas. In the North Tarim Uplift, the Cambrian source rocks experienced a prolonged oil generation process, while the Ordovician source rocks in the North Tarim Uplift and the Cambrian source rocks in the Central Uplift remained immature to low mature for a long time (Fig. 5b). As the North Depression transformed into an intra-cratonic sag, the heat flow values in the deep of the Tarim Basin kept decreasing, then briefly rose in the Middle Permian due to the TLIP event, and finally followed by a long-term decrease and formation thickening ^[59] (Fig. 5b). The impact of the Himalayan Movement on the Tarim Basin was diametrically opposite to that of the Sichuan Basin. The entire northern region underwent rapid burial, causing the Cambrian and partial Ordovician source rocks in the North Tarim Uplift to enter an ultra-deep realm ^[5] (Fig. 5b). However, at that time, the Tarim Block was located in the interior of the Eurasian continent, and had lower heat flow values for the lack of oceanic subduction (Fig. 5b). The Cambrian and Ordovician source rocks in the North Tarim Uplift remained mature to highly mature. The abrupt increase in static pressure could suppress thermal cracking of ultra-deep oil to some extent ^[6]. The Ordovician seawater had significantly lower sulfate content than that of the Permian ^[63], so the sulfate content in the Ordovician limestone reservoir in the Tarim Basin was much lower than that in the Permian dolostone in the Sichuan Basin, resulting in a weaker TSR effect on oil (Fig. 5b). Consequently, due to multiple tectonic-depositional factors, the maturity of the Ordovician and even Cambrian source rocks in the North and Central uplifts in the Tarim Basin remained in oil window, while the Cambrian-sourced oil has not yet fully cracked into gas, which ultimately induced co-enrichment of oil, condensate, and natural gas in the tectonic highs ^[64] (Fig. 6).

Sedimentary basins are essentially giant dynamic and thermochemical reactors, where temperature and pressure are not only the most critical factors controlling hydrocarbon generation, but the resulting physical and chemical forces also govern the accumulation, preservation and enrichment of oil and gas ^[6]. The ultra-deep high temperature and high-pressure conditions cause carbonate reservoirs to undergo primarily filling and compaction ^[65]. However, natural gas and acidic gases (e.g., H₂S) produced from oil TSR and thermal cracking may help preserve pores in ultra-deep environment and increase dissolution degree of pores in carbonates, which is beneficial for efficient accumulation of natural gas ^[66]. Among the ultra-deep oil and gas fields discovered in China, the highly productive giant fields are generally over-pressured, indicating ample hydrocarbon charge and superior seal integrity ^[6]. Over-pressure may be caused by hydrocarbon generation, tectonic compression and variations in geothermal field. According to the law of entropy increase, chemical processes tend to drive fluids into more disordered states. However, the exceptional source-reservoir-seal systems and contact relationships in ultra-deep strata lead to a decreased buoyancy effect of natural gas and light oil. Instead, gas and oil tend to diffuse towards low-pressure areas, exhibiting migration driving mechanisms distinctly different from those in shallow-medium and deep reservoirs ^[6].

Influenced by the intra-cratonic and long-distance compressive stress from the plate marginal strike-slip faults generated by the closure of the Paleo-Tethys and Proto-Tethys oceans, numerous strike-slip faults were developed within the Sichuan and Tarim basins ^[67-68]. During the subduction and closure of the Neo-Tethys Ocean, these strike-slip faults were reactivated and ultimately controlled the multi-layer, multi-stage and three-dimensional accumulation and enrichment of oil and gas within the basins ^[5,69] (Fig. 7). The regional large faults formed by strike-slip movement provided high-speed migration conduits for oil and gas, the twisting force of strike-slip movement further drived dispersed hydrocarbon from source rocks into reservoirs, forming low-order fractured carbonate lithological traps associated with the strike-slip faults ^[70-71]. The Himalayan Movement had two distinct impacts on the Tarim and Sichuan basins: subsidence and uplift. However, the reactivated strike-slip faults played a similar role in readjusting and re-concentrating oil and gas accumulations in the two basins ^[5] (Fig. 7). Consequently, the distribution of gas reservoirs in the Sichuan Basin is largely consistent with the trends of the Longmen Mountain and the Huaying Mountain faults (Fig. 4), while the oil and gas fields in the Tarim Basin are strictly controlled by the uplift-depression pattern, and are highly enriched along the slope-transition and fault zones (Fig. 6).

Based on the combination of geological elements for hydrocarbon accumulation and the characteristics of later tectonic evolution and adjustment, the marine ultra-deep petroleum systems in China may be categorized into three types: near-source accumulation in platform margin zones, distant-source accumulation in high-energy faults-communicated beaches, and three-dimensional accumulation in strike-slip fault zones. Most of these three types have experienced multiple stages from early accumulation to late re-adjustment (Fig. 7). There are two sources of natural gas: ancient oil cracking into gas when deeply buried, and multi-pathway composite gas from ultra-deep environment. The oil reservoirs have undergone multiple physical and chemical alterations (Fig. 7). The near-source accumulation in platform margin zones is typified by the Ediacaran- Cambrian petroleum system in the central Sichuan Basin, and the Permian petroleum systems in the northwest and northeast of the Sichuan Basin. They are characterized by the development of high-quality and large-scale source rocks in intra-cratonic rifts, and the development of mound-shoal reservoirs in the platform marginal zones. Small and medium-sized faults and unconformity planes acted as migration pathways. Multiple types of traps such as tectonic, stratigraphic and lithologic ones are developed. Oil and gas accumulate near the sources and are distributed in clusters in the platform margin zones, indicating excellent reservoir conditions. The distant-source accumulation in high-energy faults-communicated beaches is typified by the Cambrian petroleum system in the central Sichuan Basin, the Permian-Triassic petroleum system in the northeast Sichuan Basin, and the Ediacaran-Cambrian petroleum system in the Tarim Basin. They are characterized by the development of high-quality and large-scale source rocks in intra-cratonic rifts, and the development of granular beach reservoirs stacked vertically along the slopes of paleo-uplifts or distributed in ring-shapes around the paleo-rifts. Vertical and lateral large and medium-sized fractures are key factors for the accumulation of distal oil and gas. The three-dimensional accumulation in strike-slip fault zones is typified by the Cambrian-Permian petroleum system in the northwest Sichuan Basin and the Cambrian-Ordovician petroleum system in the Tarim Basin. They are characterized by large vertical faults penetrating into the high-quality source rocks of the Cambrian, and strike-slip faults not only serving as a "highway" for vertical migration of oil and gas, but also enhancing dissolution in carbonates which were developed to high-quality reservoirs with fractured and vugs. The typical characteristics are multiple hydrocarbon migrations through major faults, high oil and gas columns and obvious oil and gas enrichment.